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Sugarcane is an important sugar crop and it can be subjected to ratooning for several years. The advantages of ratooning include quality improvement, efficiency enhancement, and reduced costs and energy use. The genotype, environment, cultivation management, and harvesting technology affect the productivity and longevity of ratoon cane, with the genetic basis being the most critical factor. However, the majority of research has been focused on only limited genotypes, and a few studies have evaluated up to 100 sugarcane germplasm resources. They mainly focus on the comparison among different genotypes or among plant cane, different selection strategies for the first and second ratoon crops, together with screening indicators for the selection of stronger ratooning ability. In this paper, previous studies are reviewed in order to analyze the importance of sugarcane ratooning, the indicative traits used to evaluate ratooning ability, the major factors influencing the productivity and longevity of ratooning, the genetic basis of variation in ratooning ability, and the underlying mechanisms. Furthermore, the shortcomings of the existing research on sugarcane ratooning are highlighted. We then discuss the focus of future ratoon sugarcane research and the technical methods that will shorten the selection cycle and increase the genetic gain of ratooning ability, particularly the development of linked markers. This review is expected to provide a reference for understanding the mechanisms underlying the formation of ratooning ability and for breeding sugarcane varieties with a strong ratooning ability.

【Objective】 The effect of temperature on plant development is often characterized by degree days or accumulated temperature. In this paper, we investigate how planting date affects accumulated temperature and the consequence for the yield of two ratooning rice varieties. 【Method】 The experiment was conducted in a rice field in Changsha, central Hunan province. It included two rice varieties: Y Liangyou 900 (YLY900), which has a long growth period, and Y Liangyou 911 (YLY911), which has a moderate growth period. The seeds of both varieties were sown on March 15 (B1), March 20 (B2), March 25 (B3), March 30 (B4), April 5 (B5), or April 10 (B6) to establish a planting date gradient. In each treatment, we measured physiological parameters including growth duration, yield component, and seed-setting rate to evaluate the physiological development of the crops. 【Result】 The average annual growth period of YLY911 was 215 days. Its first and regeneration seasons were eight and ten days shorter, respectively, than those of YLY900. Delaying the planting date shortened the vegetative growth period of the first season and reduced the total growth period of both seasons in both varieties. The variation in grain yield in the first and regeneration season, as well as annual yield of YLY911, followed a parabolic relationship, peaking in B2. Conversely, the yield of YLY900 decreased steadily as planting date was delayed. Yields in the first and regeneration season, as well as annual yield, were consistently higher in YLY911 than in YLY900. The primary factors affecting grain yields were the number of ears per unit area and the seed-setting rate. With delay in planting dates, the annual accumulated temperature for both varieties first increased and then declined, peaking in B2. The accumulated temperature in the first and annual seasons for YLY900 was significantly higher than for YLY911, while the accumulated temperature in the regeneration season was lower for YLY900 than for YLY911. Such differences in the regeneration season between the two varieties were statistically insignificant (p>0.05). 【Conclusion】 For ratooning rice in our studied area, the optimal planting date was March 15 for varieties with long growth period and March 20 varieties with moderate growth period.

To promote the germination of rice panicles during the regeneration season, it is necessary to ensure a stubble height of 300–450 mm when mechanically harvesting the first-season rice. However, due to variations in the depth of the paddy soil and fluctuations in the height of the header during harvesting, maintaining the desired stubble height becomes challenging, resulting in a significant impact on the yield during the regeneration season. This study presents the design of an adaptive profiling header capable of adjusting the height and level of the header adaptively. Based on the theoretical analysis of the profiling mechanism, a quadratic regression orthogonal rotation combination experiment is designed. Considering the actual field conditions, the range of each factor is determined, and simulation experiments are conducted based on the MBD-DEM coupling to establish a mathematical regression model between each factor and indicator. In the case of the profiling wheel linkage length of 562 mm, profiling wheel width of 20 mm, and profiling wheel mass of 3.6 kg, the supporting force of the header on the profiling wheel would be greater than zero, the supporting force of soil on the profiling wheel and the depth of soil subsidence represent the smallest values, and the highest sensitivity and accuracy of the profiling wheel are achieved. Bench tests demonstrated that the header exerts a force on the profiling wheel, confirming the normal functioning of the profiling. The average magnitudes of forces exerted by the soil on the profiling wheel are obtained to be 31.98 N, 31.63 N, and 30.86 N, whereas the corresponding average soil subsidence depths are obtained as 3.4 mm, 5.6 mm, and 8.3 mm, aligning closely with the simulation values. The results indicate that the profiling mechanism achieves high accuracy in ground profiling and that the structural design is reasonable. By employing fuzzy PID control to adjust the height of the header, the average error in adjustment is obtained as 6.75 mm, while the average error in the horizontal adjustment is derived as 0.64°. The header adjustment is fast, offering high positioning accuracy, thereby meeting the harvesting requirements of the first season of ratooning rice.

Water and N management play a vital role in rice (Oryza sativa L.) production; however, limited information is available on the options to increase rice yield in rice–ratoon rice systems, including an appropriate combination of water regime (W), N application rate (NAR) and N application method (NAM). To address this question, field experiments were conducted with two Ws [simplified alternate wetting and drying (SAWD) and continuous flooding (CF)], four NARs (control, N0; 180 kg N ha−1, N180; 255 kg N ha−1, N255; and 330 kg N ha−1, N330) and two NAMs[45% of fertilizer pre‐plant, 15% of fertilizer at tilling, 40% of fertilizer at bud (BTB) and 45% of fertilizer pre‐plant, 15% of fertilizer at boot, 40% of fertilizer during grain filling (BPG)]. On average, the grain yields of the main crop, the ratoon crop, and their total for SAWD were 3.7%, 6.8%, and 4.4% higher than for CF, respectively. The relationships between NAR and the main crop, ratoon crop, and total yields were well fitted by quadratic equations. The rice yields of the main crop, ratoon rice, and their total under BPG were equal to or slightly higher than those under BTB. The interactive effect of W×NAR was significant on the main rice crop yield and total rice yield, but W×NAM, NAR×NAM and W×NAR×NAM were all related to the soil‐based yield. The use of integrated water and N management practices could achieve high yields and reduce water and N inputs in rice‐ratoon rice systems. Core Ideas The relationships between NAR and the main crop, ratoon crop, and total yields were well fitted by quadratic equations. The interactive effect of W×NAR was significant on the main rice crop yield and total rice yield, but W×NAM, NAR×NAM and W×NAR×NAM were all related to the soil‐based yield. The use of the SAWD‐N180–BPG treatment could achieve high yields and reduce water and N inputs in rice‐ratoon rice systems.

Sugarcane (Saccharum spp. interspecific hybrids), a high biomass perennial crop, in which manual data collection for early yield prediction, through its growth cycle (∼12 mo long), is labor intensive and time consuming. Alternately, aerial imagery can be explored to predict yield‐related components and high‐throughput phenotyping for genetic selection. In this study, aerial imagery and ground data were collected in Stage IV (final stage of genotype selection) of the Florida sugarcane cultivar development program to evaluate the use of unmanned aerial vehicles in yield prediction (tons of cane per hectare [TCH], sucrose concentration, and tons of sugar per hectare [TSH]) in multiple new genotypes (13 in plant cane crop, nine in first ratoon crop). Aerial imagery data were collected using hyperspectral sensor, and yield data were collected through manual sampling of sugarcane stalks at harvest. The gradient‐boosting regression tree model was selected based on low mean absolute percentage error on multiple dates (April, July, and September) to determine the best timing of yield predictions. Results showed that yield was predicted with greater accuracy in July in plant crop and April in the first ratoon crop. Also, sucrose percentage was predicted with greater accuracy (94% in plant crop and 93% in first ratoon crop) than TCH and TSH. Although only two out of the top five genotypes were common in both selection methods (measured vs. predicted yields) in Stage IV, high accuracy in TCH and sucrose percentage shows that aerial imagery may be useful in making genotype selection in early stages when actual yield estimation is not feasible. Core Ideas Data collection in sugarcane (high biomass crop) is usually labor intensive and time consuming. UAV and ML can be promising for the yield prediction and genotype selection. Yield‐related component and genotype selection were predicted in Stage IV plant and first ratoon of sugarcane. High accuracy (>90%) was observed in predicting yield‐related components using UAV‐based imaging. The results look promising to further explore the use of aerial imagery in genotype selection at early stages.

Rice (Oryza sativa L.) ratooninghas recently attracted attention due to its higher yield potential compared with that of conventional methods. Field experiments were conducted in southwestern Japan in 2019 and 2020 to determine the effect of rice type (Hokuriku 193 and high‐yielding line [HYL]) and stubble leaf treatment (clipping and control) on the grain yields of the first and second crops in rice ratooning. In 2019, both rice types produced lower grain yields of the second crop in the leaf clipping treatment than the control treatment due to the lower spikelet number m−2. Therefore, increasing the leaf area index (LAI) in the stubble may improve the grain yield of the second crop by increasing the spikelet number per area. In 2020, HYL produced a lower grain yield of the second crop in the leaf clipping treatment than the control treatment due to the lower spikelet number m−2. However, the grain yields of Hokuriku 193 did not differ between the two leaf clipping treatments. Although the nonstructural carbohydrate (NSC) content in the stubble did not differ between the two rice types in 2019, Hokuriku 193 had a higher NSC content than HYL in 2020 due to the lower spikelet number m−2 and lower percentage of filled spikelets of the first crop. These results suggest that the stubble leaf blade contribution may be reduced when the NSC content is high as the leaf blades may compensate for the lack of NSC content when the NSC content is low. Core Ideas Stubble leaf blades contribute to the spikelet number per area. Stubble leaf blades compensate for low stubble nonstructural carbohydrate content. Early maturing cultivars are recommended to avoid lower grain filling.

Due to the high rolling rate of a regular crawler paddy harvester and the absence of mature first season harvester products of ratooning rice, combined with the planting mode and harvest requirements of ratooning rice, a triangular crawler ratooning rice harvester is specifically designed. The structure and steering principle of the triangular crawler chassis are described. The hydraulic system is simulated and analyzed by AMESim2020 (Guangzhou, China) to verify the rationality of its design; RecurDynV9R4 (Guangzhou, China) is used to simulate and analyze the field straight/turning situation of differential steering chassis and rear-axle steering chassis. The results show that the rear axle steering chassis has a smaller turning radius and lower rolling loss rate and the change of track tension is more stable during steering. The field test is conducted to verify the reliability of the simulation results. The field test shows that the rolling loss rate of the rear axle steering chassis is reduced by 27.9% compared with the differential steering chassis. The machine’s operating speed is 2.8 km/h, the minimum turning radius is 780 mm, and the straight rolling rate is 26.8%. The operating performance is stable, and the operational process is smooth. Compared with the existing conventional harvester, the linear rolling rate of the first harvest of ratooning rice is reduced by 26.1%, and the test results are consistent with the RecurDyn simulation results. The results are reliable, providing a reference for the theoretical research of the chassis of the later ratoon rice harvester.

Rice (Oryza sativa L.) ratooning has recently attracted attention since it possesses higher yield potential compared to conventional rice‐growing methods; however, it requires a longer growing season. Field experiments were conducted in southwestern Japan in 2017 and 2018 to determine the effect of harvest time (early and normal) and cutting height (high and low) of the first crop on grain yield of the first and second crops using a high‐yielding line under high N application and high air temperature conditions in rice ratooning. The highest total yield of the first and second crops was produced when the first crop was harvested at the normal time with the high cutting height in 2018. This yield reached 14.4 t ha−1, which is equivalent to threefold the average yield achieved by Japanese farmers. Plants harvested at the high cutting height produced higher grain yield of the second crop because of the larger spikelet number m−2 and better grain filling using abundant leaf area index (LAI) and nonstructural carbohydrate (NSC) in the stubble. In southwestern Japan, the daily mean air temperatures during the early growth stage of the first crop and the late ripening stage of the second crop have been increasing over time. Our results suggest that increasing LAI and NSC in the stubble by harvesting at the normal time harvest with the high cutting height under high level N application conditions may provide an adaptive strategy to increase yield with a rice‐ratooning system as growing seasons extend due to global climate change.

To solve the problem of increased grain impurity rate and grain loss rate caused by clogging of sieve holes during the cleaning process of ratooning rice, a spiral step cleaning device was designed, which disturbed the flow field at the sieve holes through vortex in the slot and disrupted the force balance of the blockages at the sieve holes. The device mainly includes a cleaning separation core and a cleaning separation core shell. Firstly, the main parameters of the cleaning separation core were determined, and the critical shear airflow velocity was obtained through theoretical analysis. Through energy loss analysis, the fan wind speed was determined to be 11.5 m/s. Secondly, the CFD-DEM coupling method was used to analyze the flow patterns inside the slot and the movement patterns of blockages on the sieve surface, confirming the effectiveness of vortex guided blockage removal. Finally, a prototype was designed and built for testing, and the results showed that when the wind speed of the fan was 11.5 m/s, the grain impurity rate was 1.35%, the grain loss rate was 2.13%, and the average sieve blockage rate was ≤0.1%. All indicators were better than traditional cleaning devices and could meet the cleaning requirements. During the continuous operation of the spiral step cleaning device, performance indicators such as sieve hole blockage rate remained basically unchanged.

Grain-filling of rice spikelets (particularly for the later flowering inferior spikelets) is an important characteristic that affects both quality and yield. Rice ratooning technology is used to cultivate a second crop from dormant buds that sprout from stubble left after the first harvest. This study used two rice varieties, the conventional indica rice ‘Jinhui 809’ and the hybrid indica-japonica rice ‘Yongyou 1540’, to assess the impact of rice ratooning on grain-filling. The results indicated that the grain-filling process in inferior spikelets of ratoon season rice (ISR) showed significant improvement compared to inferior spikelets of main crop (late season) rice (ISL). This improvement was evident in the earlier onset of rapid grain-filling, higher seed-setting percentage, and improved grain quality. A label-free quantitative proteomic analysis using mass spectrometry identified 1724 proteins with significant abundance changes, shedding light on the molecular mechanisms behind the improved grain-filling in ISR. The functional analysis of these proteins indicated that ratooning stimulated the metabolic processes of sucrose-starch, trehalose, and hormones in rice inferior spikelets, leading to enhanced enzyme activities related to starch synthesis, elevated concentrations of trehalose-6-phosphate (T6P), indole-3-acetic acid (IAA) and zeatin riboside (ZR) during the active grain-filling phase. This research highlighted the importance of the GF14f protein as a key regulator in the grain-filling process of ISR. It revealed that GF14f transcriptional and protein levels declined more rapidly in ISR compared to ISL during grain-filling. Additionally, the GF14f-RNAi plants specific to the endosperm exhibited improved quality in inferior spikelets. These findings suggest that the enhancement of starch synthesis, increased levels of IAA, ZR, and T6P, along with the rapid decrease in GF14f protein, play a role in enhancing grain-filling in ratoon season rice.